1. Field of the Invention
The present invention relates to a signal modulation method and a signal rectification and modulation device, and more particularly, to an alternation-type signal modulation method and a related signal rectification and modulation device.
2. Description of the Prior Art
For safety purposes, a power supply device of an induction type power supply system has to ensure that a proper power receiving device is positioned on the sensing area of a supplying-end coil of the power supply device, and that the power receiving device is ready to receive power before the power is supplied. In order to allow the power supply device to confirm the above conditions, a data code should be transmitted for identification purposes. The data code transmission is performed via the following steps: the power supply device drives the supplying-end coil to generate resonance and sends electromagnetic power to the power receiving device in order to transmit power. When the power receiving device receives the power, the power receiving device may change the impedance on the receiving-end coil via the signal modulation technology, and the variations are fed back to vary the amplitude of carriers on the supplying-end coil.
The data code is composed of a plurality of modulation signals. In the prior art, the power receiving device performs signal modulation on both terminals of the induction coil at the same time. For example, as shown in the receiving-end module 20 of U.S. Publication No. 2013/0342027 A1, the receiving-end microprocessor 21 simultaneously turns on the switches A6 and B6 respectively corresponding to the two terminals of the induction coil, in order to perform modulation on both terminals of the induction coil simultaneously. In detail, during a modulation period, the switches A6 and B6 may be turned on simultaneously, so that the signal modulation resistors A3 and B3 may perform modulation simultaneously. At this moment, due to operations of the control diodes A4 and B4, the low-side switches A2 and B2 may stop performing rectification at the same time. In such a situation, in order to increase the amplitude of the signals reflected to the supplying-end coil, the modulation time should be increased, which prolongs the time when the rectifier stops operating, such that the power supply capability for the back-end circuits may be reduced. On the other hand, the signals reflected to the power supply device may become larger when the resistance values of the signal modulation resistors A3 and B3 become smaller, and this also brings about a larger power loss during the modulation period. In other words, another method to realize the amplification of reflection signals is to reduce the signal modulation resistors, but the reduction range is still limited to the bottleneck of power loss.
In addition, the low-side switches A2 and B2 for performing rectification are connected to the induction coil via the protection resistors B1 and A1, respectively. The gate voltages of the low-side switches A2 and B2 are controlled by the coil voltage, so that the low-side switches A2 and B2 may be turned on or off to perform rectification operations. However, in order to increase the operational speed of the low-side switches A2 and B2, the resistance values of the protection resistors A1 and B1 should be reduced to increase the charging/discharging speed on the gate terminals of the low-side switches A2 and B2. In such a condition, the protection resistors A1 and B1 having a lower resistance value will cause the zener diodes A5 and B5 to accept larger power and thus to be burnt easily. As a result, the switching speed of rectification is also limited.
On the other hand, in the receiving-end module 20 of U.S. Publication No. 2013/0342027 A1, the voltage stabilizer circuit 25 applies the regulating capacitor 251 to stabilize the output voltage. Since the regulating capacitor 251 always has a larger capacitance, the protection circuit breaker 24 is disposed between the regulating capacitor 251 and the rectifier and signal feedback circuit 23, in order to allow power to be used by the receiving-end microprocessor 21 first and prevent the regulating capacitor 251 from absorbing too more charges causing that the receiving-end microprocessor 21 fails to be turned on when the supplying-end module 10 and the receiving-end module 20 start to interact and the rectifier and signal feedback circuit 23 starts to output power. In addition, when the receiving-end coil 271 just departs from a power supply device, there are still a large number of charges existing in the regulating capacitor 251. These charges may flow back to the receiving-end microprocessor 21 to cause the receiving-end microprocessor 21 unable to determine whether it is in a power supply phase. Moreover, the above circuit structure may possess another problem. When the receiving-end module 20 just detects that power arrives, the protection circuit breaker 24 is turned off; that is, the rectifier and signal feedback circuit 23 is not connected to a large capacitor (i.e., the regulating capacitor 251) which is able to help receive charges, such that an instant high voltage input may burn the circuit elements. In addition, at the instant where the protection circuit breaker 24 is turned on, the regulating capacitor 251 starts to receive a large number of charges, which instantly decreases the operation voltage of the receiving-end microprocessor 21, and thereby causes the receiving-end microprocessor 21 to stop operating or generates other ill effects.
Please refer to FIG. 1, which is a waveform diagram of signal modulation. As shown in FIG. 1, the waveform W1_1 illustrates signals on the gate terminals of the switches A6 and B6 in the receiving-end module 20 described in U.S. Publication No. 2013/0342027 A1, where the signals simultaneously turn on the switches A6 and B6 in a high voltage level, in order to generate modulation signals. The waveform W1_2 illustrates signals obtained from the modulation signals reflected to the power supply device and then processed by the signal analysis circuit 13. As shown in the waveform W1_2, the signals in the power supply device fed back from every modulation signals vary in amplitude, this is because the modulation control signals (i.e., the signals on the gate terminals of the switches A6 and B6) are not synchronous with oscillation cycles of the coil. In other words, the modulation signals randomly occur on the oscillation cycles of the supplying-end coil. Therefore, the starting point corresponding to the oscillation cycles and the oscillation number of times reflected to the supplying-end coil in each modulation period are not fixed, such that the amplitude variations on the supplying-end coil due to signal modulation are not fixed as well. In U.S. Publication No. 2013/0342027 A1, the power supply device may automatically adjust the voltage level for signal determination according to signal variations on the coil, so signal variations with different amplitudes may easily cause wrong determination.
Furthermore, please refer to FIG. 2, which is a waveform diagram of signals in a signal modulation period. As shown in FIG. 2, the waveform W2_1 illustrates signals on the gate terminals of the switches A6 and B6 in the receiving-end module 20 described in U.S. Publication No. 2013/0342027 A1, where the signals simultaneously turn on the switches A6 and B6 in a high voltage level, in order to generate modulation signals. The waveform W2_2 illustrates the gate voltage of the low-side switch B2. As shown in FIG. 2, during the modulation, operations of the control diodes A4 and B4 allow the low-side switches A2 and B2 to stop performing rectification simultaneously; that is, the gate voltage of the low-side switches A2 and B2 should be zero, in order to turn off the low-side switches A2 and B2. As shown by the waveform W2_2 in FIG. 2, however, a voltage still remains in the gate terminal of the low-side switch B2 and the gate voltage does not exactly reach a zero voltage and keep on the zero voltage during the modulation period (i.e., the period where the signals on the gate terminals of the switches A6 and B6 are in the high voltage level). Therefore, the low-side switch B2 cannot be fully turned off, such that redundant power consumption is generated during the modulation process.
As can be seen, many problems in the prior art still need to be solved. Thus, there is a need to provide a signal modulation method, which allows the receiving-end module to generate modulation signals more effectively and also overcome the above drawbacks.